1. Field of the Invention
This invention relates to a structure for supporting a head, and particularly to a head supporting structure for supporting a video head in a video tape recorder ( VTR ) system.
2. Description of the Prior Art
In a VTR system, a video head scans tape along a track formed thereon, and when the head deviates from the track, the head is moved with respect to the tape in the transverse direction of the track thereby bringing the head back into registry with the track, so that a so-called tracking operation is carried out. Typically, a head is mounted at a tip end of piezo-electric element which is fixedly attached to a head bar, head disc or rotating cylinder, and when a deviation of the head from a predetermined track on tape is detected, a voltage proportional to the amount of deviation is applied to the piezo-electric element thereby moving the head back into registry with the track. And, such a piezo-electric element is typically comprised of a bimorph cell which includes two piezo-electric plates overlaid opposite in polarity and sandwiched by three electrode layers with the sandwiched electrode layer connected to one terminal and the pair of sandwiching electrode layers commonly connected to the other terminal, whereby a voltage is applied between the terminals.
FIGS. 1a and 1b show a typical prior art head supporting structure in a VTR system. As shown, the supporting structure includes a rotary cylinder 4 to which one end of a piezo-electric element 1 is fixedly attached through a fixture element 3 by means of a screw 2, and a head 5 is fixedly mounted at the free end of the piezo-electric element 1. There is also provided another cylinder 6 opposite to the cylinder 4, and the head 5 is so located to slightly project toward outside with respect to the peripheral surface defined by these opposed cylinders 4 and 6. It is to be noted that since this is a two-head system, there is a pair of heads 5, 5 located diametrically opposite to each other.
In FIG. 1a, tape travels around the cylinders 4 and 6 slightly aslant and the head 5 moves along a circle. And, when a voltage is applied to the piezo-electric element 1 for tracking operation, the piezo-electric element 1 deflects either upward or downward depending on the direction of the voltage applied thereby causing the head 5 to move up and down correspondingly.
In the above-described structure, however, the amount of vertical shift of head 5 is proportional to a distance 1.sub.1 from the fixture point to the free end of the piezo-electric element 1 and a voltage applied to the element 1. Thus, if it is desired to make the cylinder 4 smaller in diameter, the distance 1.sub.1 becomes smaller and thus the shift amount of head 5 is reduced, thereby making it impossible to attain a sufficient tracking function. This has long been one of the obstacles in making the head cylinder and thus the overall VTR system compact in size.